This invention relates to the manipulation of porous fabrics, and more particularly, relates to the manipulation of "fiberglass" cloth, roving, chopped strand mat and continuous random mat during their assembly as primary reinforcement material in fiber reinforced plastic (FRP) articles of manufacture.
In many of these assembly operations pre-cut sheets of the fabrics having the desired shapes are stacked. If several fabrics will be used in the article, several corresponding stacks of the different fabrics are centrally located relative to the assembly operation. In a typical process for assembly of fabrics into a finished article, the "hand layup" method is used, wherein manual labor is used to assemble the different fabrics in a preferred order.
Since the invention therefor envisions the manipulation of sheets of material, a review of the prior patent literature is advisable. Note for example U.S. Pat. No. 3,362,706 wherein a flexible vacuum plate member is used to pick up stacked mailing envelopes. More specifically, this invention relates to apparatus for separating flat articles one at a time, and, more particularly, to apparatus for pneumatically removing the top article of a stack of such articles and preventing double and multiple removals.
The apparatus includes a suction head which is connected to a vacuum source and which is comprised of at least two sections which are moveable with respect to one another. The two sections of the suction head are advanced into engagement with the uppermost article of the stack. A partial vacuum is then applied to the suction head so that the uppermost article is held against the suction head. One of the sections is restrained while the other is retracted under the influence of atmospheric pressure. This causes the article to be bent around the edges of the sections of the suction head whereupon any additional articles which might adhere to the uppermost article fall back into the stack.
Additionally, a limit stop may be provided which engages the edge of the uppermost article which is being lifted by the suction head to bend the article into a generally S-shaped configuration. The restraining device is then released so that the two sections become aligned, permitting the separated article to assume again a generally flat configuration.
Reference also, for example, U.S. Pat. No. 3,415,388 which discloses a device for the removal of pre-shaped foils from a foil stack and insertion into production moulds, in installations for the production of foil-wrapped chocolate bodies. For obliquely arranged stacks of preshaped foils, the device has a suction head that is obliquely guided by a stationary guide rail against the bias of a spring. The suction head is geometrically similar to the preformed foil bodies and is three-dimensionally reduced with respect thereto at least in the outer edge region by multiple of the foil thickness, for example 1-2 millimeters to produce a gap having a wedge shape in cross-section.
Note that both of the previously referenced patents do not disclose manipulation of porous fabrics.
Other patents of interest would include U.S. Pat. No. 4,483,702 wherein a porous fiberglass cover is used with a vacuum holder system so as to provide passage for residual air and adjacent passages that ten to equalize when a sheet of glass is held against the porous cover. The apparatus is used to manipulate sheets of matter such as glass sheets, as also taught in U.S. Pat. No. 4,511,387, same assignee.
Reference may also be made to U.S. Pat. No. 3,848,752 wherein an apparatus for transferring glass sheets comprises a sequence of drive rollers above the transfer path and suction means arranged to draw the sheets against the rollers so that the sheets are advanced by the rollers. In order to release a sheet onto a stack, when the sheet has reached a predetermined position along the path, suction release means may be provided or mechanical means may be provided to force the sheet away from the rollers.
Reference may also be made to U.S. Pat. No. 3,780,884 which discloses an article transfer device comprising a first conveyor, a platform positioned to permit transfer of articles between said platform and said first conveyor, a vacuum manifold mounted above said platform, a plurality of vacuum cups depending from said manifold and each having a bore communicating the gripping surface thereof with said manifold, elevating means for raising and lowering said platform into and out of a position to cause articles carried by said platform to engage at least one of said vacuum cups, a shuttle extendable to a position underlying said vacuum cups and retractable to a position removed from said vacuum cups, and a second conveyor positioned to permit transfer of articles between said shuttle and said second conveyor.
Reference may also be made to U.S. Pat. No. 2,798,757 wherein this invention relates to improvements in articles handling and lifting apparatus. It is more particularly designed for grafting, lifting and transferring groups of small variable-sized articles such as eggs.
Referring now also to (prior art) FIGS. 1A through 1D is should be noted that Singer Sewing Company has several fabric manipulation devices that are designed for manipulation of apparel fabric from soft muslin or lace to a heavier material such as denim. These devices do not work reliably in all cases for fiberglass fabric because of the open weave, random structure, porosity and entanglements between adjacent fibers. The long needle 90 shown in FIG. 1A has difficulty maintaining a grip on the fabric after pickup. The Cardin wheel 92 shown in FIG. 1B induces fabric pattern distortion if the Cardin travel is not controlled properly. The soft tooth pincher 94 shown in FIG. 1C causes the glass filaments to break when subjected to the pinching action. The barbed needle 96 shown in FIG. 1D is hard to retract from the fabric after the needle has penetrated the fabric if the needle remain protruded under normal conditions as is the present case. It can therefore be seen that wherein several apparatus have been developed to manipulate fabrics commonly used in the textile industry these same apparatus cannot be successfully used in all cases to manipulate different varieties of fiberglass fabric.
A process therefore needs to be developed that results in the manipulation of one sheet, or a plurality of sheets of different porous fiberglass fabric(s). The apparatus used in the process should be capable of repeatable operation to lend itself to the economic assembly of articles of manufacture.